Automatic volume control



Fb. 17,1970 G. J. VbLLmK 3,496,452

u AUTO MATIC VOLUME CONTROL Filed Nov. 8, 1966 2 Sheets-Sheet 1 Ian a? 1N INVENTOR.

2 Gi/beri J Vo///m( BY ,(Mmwfa m/ RTTORN E Y5 Feb. 17', 1910 v G, J.VOLLINK 3,496,452

AUTOMATIC VOLUME CONTROL Filed Nov. 8. 1966 INVENTOR.

Gi/berf J. Vo/b'n" ATTORNE Y5 United States Patent 3,496,452 AUTOMATICVOLUME CONTROL Gilbert J. Vollink, Grand Rapids, Mich., assignor, bymesne assignments, to Rowe International, Inc., Whippany, N.J., acorporation of Delaware Filed Nov. 8, 1966, Ser. No. 592,896 Int. Cl. Gf1/40 US. Cl. 32321 15 Claims ABSTRACT OF THE DISCLOSURE A fast attacktime, relatively slower release time automatic volume control circuitcomprises a main capacitor which normally provides a regulating voltagefor a lamp, the brightness of which controls the amplitude of an outputsignal, which may be of audio frequency, as from a record player.Whenever the output signal amplitude exceeds a certain level, anauxiliary capacitor immediately discharges. It then recharges from themain capacitor to produce a rapid and predetermined reduction in theoutput signal amplitude.

Background of the invention There are known in the prior art coinoperated automatic record playing devices or jukeboxes. These devicesare required to play a great variety of various brands, sizes and speedsof records.

In playing a record the background level and the sound level are afunction of the depth of the needle grooves and the amount of lateralmovement permitted for the needle. The lateral movement in turn is afunction of spacing between adjacent grooves on the record. This groovespacing not only varies from manufacturer to manufacturer but, also, itvaries with one manufacturer depending upon the amount of recordedmaterial he desires to fit onto a single record.

It will readily be apparent from the foregoing description that formaterial of relatively short duration on a single disk, wide spacingsare employed and a relatively high sound level is readily attained. Onthe other hand, where material of long duration is compressed onto asingle record disk, the spacing between the grooves must of necessity besmall and the resultant sound level is consequently low. This latterproblem is of special importance in the use of small, long-play recorddisks now widely used in jukeboxes.

Coin-operated automatic record players of the type described above mustbe able to play records of all the types described above which may bemixed in the same machine and it must play them with approximately thesame audio output level.

In an attempt to solve the problem of playing various records havingdiiferent groove spacings in machines of the prior art, there isprovided an automatic volume control arrangement in which the amount ofsignal shunted from the output is determined by the illumination of alamp which lights a photo-responsive device. In a system of this type, asignal level responsive circuit provides a voltage for the lamp whichincreases with increasing sound level to shunt more of the sound tolimit the output sound level. It may be a capacitive circuit whichdischarges in response to signal level above a predetermined level.

For proper operation of a circuit of the type described, the attacktime, or time required to produce a lamp voltage change in response to asignal level change, cannot be too long or pulses of sound, or envelopepulses, will not permit a sufficient change in capacitor voltage to givea significant decrease in lamp voltage. On the other hand, the attacktime cannot be too short since the lamp has an inherent lag inresponding to change in the voltage applied thereto. In other words, thelamp illumination will not change immediately with a change in thevoltage applied thereto. As a result, the attack time, while not beingtoo long, should be appreciably longer than the lag in lamp response.

I have invented an improved automatic volume con trol circuit whichsolves the problems outlined above. My' circuit has a relatively shortattack time While maintaining a relatively long release time, or timerequired for the circuit to return to equilibrium after a lamp voltagechange. My automatic volume control circuit is especially adapted foruse in jukeboxes. It minimizes the undesirable effect of sharp pulses ofshort duration in the sound level of the output. It provides anarrangement wherein the attack and release time of the circuit canindependently be controlled. It provides a very constant output.

Description of the invention One object of my invention is to provide anautomatic voltage control circuit having a fast attack time and having arelatively slow release time.

Another object of my invention is to provide an automatic voltagecontrol circuit which is especially adapted for use in jukeboxes.

A further object of my invention is to provide an automatic voltagecontrol circuit which responds to relatively sharp pulses of sound levelof short duration.

A still further object of my invention is to provide an automatic volumecontrol circuit having a very constant output.

Other and further objects of my invention will appear from the followingdescription.

In the accompanying drawings which form part of the instantspecification and which are to be read in conjunction therewith and inwhich like reference numerals are used to indicate like parts in thevarious views:

FIGURE 1 is a schematic view of one form of my automatic volume controlcircuit.

FIGURE 2 is a schematic view of an alternate form of the output signallevel responsive portion of my automatic volume control circuit.

FIGURE 3 is a schematic view of a further form of the output signallevel responsive portion of my automatic volume control circuit.

FIGURE 4 is a schematic view of a still further form of the outputsignal level responsive portion of my automatic volume control circuit.

Referring now to FIGURE 1 of the drawings, one form of my automaticvolume control circuit includes a suitable source of potential having aterminal 10 providing a voltage of, for example, 30 volts. The soundsystem of the device such, for example, as a jukebox with which myautomatic volume control circuit is employed, includes a terminal 12 towhich the signal from the pickup or the like is applied. A capacitor 14couples this signal to the base of an amplifier transistor 16 having acollector resistor 18 connected to terminal 10 and having an emitterresistor 20 connected to ground. Voltage dividing resistors 22 and 24provide a bias for the base of the transistor 16. A resistor 26 couplesthe output signal of the amplifier 16 to the base of a transistor 28 andto one terminal of a shunting filter including a capacitor 30 and aphoto-responsive resistor 32, the other terminal of which is connectedto ground. As will more fully be explained hereinafter, the resistor 32is disposed in a light-tight housing 34 together with a lamp 36 adaptedto illuminate the resistor.

Transistor 28 has an emitter resistor 38 which provides the audio outputsignal at an output terminal 40. A filter capacitor 42 connected inseries with a resistor 44 having a brush 46 and a resistor 48 betweenterminal 40 and ground provides a voltage at the brush 46 which is ameasure of the sound level at the output terminal 40.

I apply the signal on brush 46 to the base of a silicon transistor 50having a silicon diode 52 connected between its emitter and ground. Aresistor 54 connected between terminal 10 and diode 52 provides abiasing voltage .for the diode. Transistor 50 has an inherent base toemitter delay of about one half volt while diode 52 also provides a onehalf volt delay with the result that there is an overall delay of onevolt at brush 46 before transistor 50 is rendered conductive. I connecta resistor 56 and the main control capacitor 58 in series betweenterminal'l and ground. A resistor 60 connects the common terminal ofresistor 56 and capacitor 58 to the collector of transistor 50. Iconnect the first auxiliary capacitor 62 and a resistor 64 between thecollector of transistor 50 and ground. A diode 66 shunts resistor 64 tocontrol charging of capacitor 62 in a manner to be described. The secondauxiliary capacitor '68 shunts transistor 50 and diode 52. The signal oncapacitor 58 is coupled to the base of an amplifier-transistor 72, theemitter of which is coupled to the base of a second amplifier-transistor74, the emitter of which is grounded through resistor 77. Transistors 72and 74 have a common collector resistor 76. A conductor 78 applies thecollector output voltage of transistor 74 to the lamp 36 through al-volt Zener diode 79.

In one form of my automatic volume control circuit, resistor 56 willhave a resistance of megohms. The collector resistance of transistor 50with the device nonconductive may be approximately 10 megohms. Resistors60 and 64 have respective resistances of K and 90K, while resistors 76and 77 have respective values of 670 ohms and 330 ohms. Capacitors 58,62 and 68 have respective values of 50 i, 9 pf and 1 pf. The currentgains of transistors 72 and 74 are 170 each.

The input impedance of emitter follower transistor 72 will therefore be(330) l70) =l0 megohms, as indicated in FIGURE 1.

Considering the circuit with the particular circuit parameters justdescribed and with transistor 50 not conducting, capacitors 58, 62 and68 charge to a potential of 10 volts. The time-constant for this charge,which timeconstant is the release time of the circuit, Will be theequivalent resistance, which is approximately 3.3)(10 ohms, times thetotal capacitance, which is 60 10 farad, giving a time constant of 3.3minutes. It will readily be apparent that the release time thus isrelatively long. With the capacitor '58 thus charged, transistors 72 and74 will each have an emitter potential of substantially 10 volts; andtransistor 74 will draw 30 ma. collector current. Accordingly transistor74 will approach saturation with a collector potential of substantially10 volts. However no signal is applied to lamp 36 because of the 10 voltdrop in potential provided by Zener diode 79. Under these conditions theresistance of the device 32 is high and very little signal is shuntedfrom the output at terminal 40.

Assume now that there is a relatively steady level of sound input whichproduces more than 1 volt at brush 46 and thus renders transistor 50conductive. Capacitors 62 and 68 now discharge very rapidly. Capacitor58 continues to discharge through resistor 60 and transistor 50 with atime constant of 20 10 50 l0 or one second, which is the attack time ofthe circuit. This attack time, while being short, is relatively longcompared with the lag in the response of lamp 36 which may, for example,be about 0.25 second. Capacitor 68 provides a low impedance tomoderately low audio frequencies so that the collector of transistor 50is maintained substantially at ground potential even though transistor50 is gated on only during the positive peaks of the audio signal.

As capacitor 58 discharges in the manner described above, conductionthrough transistors 72 and 74 is reduced, increasing the voltage appliedto the lamp, and

increasing the illumination of resistor 32 to reduce its resistance andshunt more of the signal input of transistor 28 to ground. The signal atbrush 46 is thus attenuated until it is only slightly in excess of onevolt peak value.

'A steady state condition is reached with transistor 50 driven slightlyinto conduction at the positive peaks. Transistor 50 now acts more as agated amplifier than as a true switch, since it will not be driven tosaturation.

As a voltage amplifier, transistor 50 has an extremely high gain becauseof the large collector resistance. However voltage 50 provides a verylow power output which is not sufficient to operate the lamp. Thenecessary power gain is provided by cascaded emitter followers 72 and74. This power gain is achieved with negligible drift since the voltagegains of the emitter followers are substantially unity irrespective ofwide variations in their current amplification factors by virtue of thelarge degenerative or negative feedback. Transistor 74 of courseprovides a voltage gain of two at its collector output; but this smallvoltage gain is insignificant compared with the large voltage gain ofthe delayed, gated-amplifier 50. The performance of any delayedautomatic volume control increases with the extent of amplificationafter the delay level is exceeded, provided such amplification isrelatively free of drift. If such amplification is subject to drift,then the AVC system will be either rendered completely inoperative orsubject to erratic operation depending upon whether the amplifier hangsup or saturates at one limit or the other. My AVC system provides highgain with low drift. The output signal at terminal 40 varies less than 1db for inputs at terminal 12 ranging from 0.6 millivolt to mv.

Considering now the occurrence of a single short pulse in the inputsound level as represented by its envelope, transistor 50 is renderedconductive for the duration of the pulse. When that occurs, capacitors62 and 68 immediately discharge. Then capacitor 68 rapidly rechargesfrom capacitor 58 through resistor 60 with a time-constant of 20milliseconds. This removes 2% of the charge from capacitor 58 whichproduces a sharp small drop in conduction of transistors 72 and 74, andcorrespondingly, a sharp small increase in the voltage applied to lamp36. Then capacitor 62 recharges from capacitor 58 at a rate determinedby the total resistance 20K+90K and the capacitance 9 M3. in thecharging circuit, or with a time constant of approximately one second,which is the same as the attack time of the system. With this sequenceof events, the portion taken from the total charge of capacitor 58 isthe ratio of the sum of the capacitances of capacitors 62 and 68 to thetotal capacitance in the circuit, or about 0ne-sixth of the totalcharge. The signal at terminal 40 is correspondingly reduced byapproximately 16.7% which represents a power attenuation of 0.8 db.

Assuming now a number of short imput pulses occurring within a periodless than one second, transistor 50 is rendered conductive during eachof these pulses. Upon each pulse, capacitor 68 instantaneouslydischarges and then rapidly recharges from capacitor 58, thus reducingthe charge thereon by about 2%. After the last pulse, capacitor 62recharges from capacitor 58 through resistors 60 and 64. The totalvoltage attenuation is 2% (n1)+16.7%; and the total power attenuation is0.1 db (n1)+0.8 db, where n is the number of pulses.

Referring now to FIGURE 2, I have shown an alternate form of the signalresponsive portion of my automatic volume control circuit. In thearrangement shown in FIGURE 2, I replace the resistor 60 with a resistor'80 rather than the 20K resistor 60 as in FIGURE 1. having a value of Kbetween capacitor 58 and the diode 66. With these changes, the dischargepath for capacitor 58 includes the parallel-connected resistors 80 and82 which, as will readily be appreciated, provide the same one secondattack time as does the form of my cir-\ cuit shown in FIGURE 1. Therecharging circuit for audio-filtering capacitor 68 comprises the 25Kresistor 80 rather than the 20K resistor 60 as in FIGURE 1. The single110K resistor 82 of FIGURE 2 replaces the series-connected resistors 60and 64 of FIGURE 1 in the recharging path for capacitor 62. In all otherrespects, the circuit is the same as that shown in FIGURE 1.

Referring to FIGURE 3, I have shown one arrangement in which I connectcapacitors 84 and 86 in series rather than in parallel as is the casewith capacitors 62 and 68 in FIGURES 1 and 2. Diode 66 is connecteddirectly between the common terminal of capacitors 84 and 86 and thecollector of transistor 50. A resistor 88 shunts capacitor 86. In thisform of my circuit I select capacitors 84 and 86 to have respectivevalues of 10 f. and 1 ,uf. and I select resistor 88 to have a value of80K. The discharge path for capacitor 58 is through the 20K resistor 60as in FIGURE 1. Moreover, the 1 ,uf. audio filtering capacitor 86recharges through the same resistor. However, the capacitor 84 chargesthrough the series connected resistors 60 and 88 from capacitor 58. Thetime constant in this case will be the same as in the form of theinvention shown in FIG- URE 1.

FIGURE 4 illustrates a modified form of the seriesconnected capacitorcircuit shown in FIGURE 3. In this form of the device, a 25K resistor 80connects capacitor 58 to the collector of transistor 50. A resistor 92having a value of 100K connects capacitor 58 to the anode of diode 66.The discharge circuit of capacitor 58 includes the parallel connectedresistors. 80 and 92 providing a discharge time-constant of one second.Capacitor 86 recharges from capacitor 58 through the 25K resistor 80while capacitor 84 recharges from capacitor 58 through the 100K resistor92.

In each of FIGURES 2, 3, and 4, the delay bias is only one half volt asprovided by silicon transistor 50, since silicon diode 52 has not beenemployed. Also transistor 72 is now assumed to have a current gain of300. Only one emitter follower power amplifier is used; and its emitterresistor 77 has a value of 33K. The emitter follower input impedance is33 10 300=l megohms as indicated in each figure. The collector resistor76 has a value of 67K, which is assumed to be sufficiently low tooperate a sensitive lamp. In the absence of an input signal, transistor72 will be just at saturation and draw a conduction current of 0.3milliampere. The collector output of transistor 72 will exhibit avoltage gain of two as determined by the ratio of collector and emitterresistors 76 and 77. Again excellent AVC performance is achieved becauseof the extremely high voltage gain of delay amplifier 50 and thelow-drift power gain of degenerative amplifier 72.

In operation of my automatic volume control circuit with no signalinput, the capacitors 58, 62 and 68 charge to a potential of aboutvolts. Transistors 72 and 74 conduct relatively heavily to reduce thevoltage on lamp 36 to a point at which the lamp is extinguished. Uponthe application of an input signal to the circuit which produces morethan the delay voltage at brush 46, transistor 50 is gated intoconduction, discharging audio filtering capacitor 62 to groundpotential. For steadystate input signals, capacitor 58 discharges with atime constant of one second to increase the lamp voltage and reduce theresistance of element 32 until the output signal from transistor 28 isattenuated sufiiciently that transistor 50 is nearly extinguished.

For pulsed input signals of a duration appreciably less than theone-second attack response time of the system, an arbitrary reduction ingain is made. This arbitrary reduction is fairly large, subject to thelimitation that it not be objectionable to the listener. Accordingly thearbitrary attenuation may be of the order of magnitude of approximately1 db which is the sensitivity of the normal human ear. It is desiredthat this attenuation be substantially the same irrespective of thenumber of pulses within a one-second period. This is achieved by makingcapacitor 62 large compared with audio filtering capacitor 68 in FIGURES1 and 2, or by making capacitor 84 large compared with audio filteringcapacitor 86 in FIGURES 3 and 4, and by providing diode 66 to insurethat capacitor 62 or 84 can instantaneously discharge through transistor50 but can recharge only through the high resistance of resistor 64, 82,88, or 92 rather than merely through the low resistance of resistor 60or 80.

It will be seen that I have accomplished the objects of my invention. Ihave provided an automatic volume control circuit having a relativelyshort attack time and a relatively long release time. It is especiallyadapted for use in jukeboxes to permit them to play a wide variety oftypes and brands of record disks at substantially the same output level.My circuit minimizes the undesirable effects of sharp pulses of shortduration in the output sound level. My circuit provides excellentregulation of output over a wide range of inputs.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of myclaims. It is further obvious that various changes may be made indetails within the scope of my claims without departing from the spiritof my invention. It is, therefore, to be understood that my invention isnot to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. An automatic volume control circuit for regulating an output signalincluding in combination, a variable gain element providing said signal,means comprising a capacitor for controlling said element, means forcharging said capacitor with a relatively long timeconstant, and meansresponsive to an output signal exceeding a certain value for dischargingthe capacitor with a relatively short time-constant, the controllingmeans comprising means responsive to charging of the capacitor forincreasing the gain of the element and responsive to the capacitor fordecreasing the gain of the element.

2. An automatic volume control circuit for regulating an output signalincluding in combination a variable gain element providing said signal,a first transistor having a base and an emitter and a collector, meansapplying said signal to the base, means for maintaining the emitter atsuch fixed potential that the transistor is conductive only for outputsignals exceeding a certain amplitude, means including a resistor ofvery high resistance for connecting the collector to a source ofvoltage, a storage capacitor, means coupling the capacitor to thecollector, the transistor and the resistor comprising a groundedemittergated amplifier, and means responsive to the voltage drop betweencollector and emitter of the transistor for controlling said element,the controlling means comprising means responsive to a large voltagedrop for providing a high gain and responsive to a small voltage dropfor providing a low gain.

3. A circuit as in claim 2 in which the controlling means comprises asecond transistor having a base and an emitter, means connecting thecollector of the first transistor to the base of the second transistor,and means including a resistor of appreciable resistance for con nectingthe emitter of the second transistor to a voltage source.

4. An automatic volume control circuit for regulating an output signalincluding in combination, a variable gain element providing said signal,means comprising a control capacitor for controlling said element, anauxiliary capacitor, means for charging said control capacitor and saidauxiliary capacitor with a relatively long-timeconstant, and meansresponsive to an output signal exceeding a certain value for dischargingthe control capacitor with a predetermined and relatively shorttimeconstant and for substantially instantaneously discharging theauxiliary capacitor.

5. A circuit as in claim 4 in which said element has a response lag andin which said predetermined timeconstant is appreciably greater thansaid lag.

6. A circuit as in claim 4 in which said control capacitor has a muchlarger capacitance than said auxiliary capacitor.

7. A circuit as in claim 4 in which the charging means comprises meansfor charging the auxiliary capacitor from the control capacitor with atime-constant approximately the same as said predeterminedtime-constant.

8. A circuit as in claim 4 in which the means for discharging thecontrol capacitor comprises a resistor 'having a relatively lowresistance, in which the charging means for the control capacitorcomprises a resistor having a relatively high resistance, and in whichthe charging means for the auxiliary capacitor comprises a resistor ofintermediate resistance coupling the control capacitor and the auxiliarycapacitor.

9. A circuit as in claim 4 in which said signal responsive meanscomprises a device providing a very low impedance in response to anoutput signal exceeding such value and means including a rectifier forshunting said device across said auxiliary capacitor.

10. An automatic volume control circuit for regulating analternating-current output signal including in combination, a variablegain element providing said signal, means including a control capacitorhaving a relatively large capacitance for controlling said element, afirst auxiliary capacitor having a relatively low capacitance, a secondauxiliary capacitor of intermediate capacitance, means including a firstresistor having a relatively large resistance for charging the controlcapacitor, a device providing a very low impedance in responseto anoutput signal exceeding a certain value, means including said device anda second resistor having a relatively low resistance for discharging thecontrol capacitor, means including a third resistor of intermediateresistance for charging the second auxiliary capacitor from the controlcapacitor, means including said device and a rectifier for dischargingthe second auxiliary capacitor, and means including the first of theauxiliary capacitors for providing a capacitive shunt across the device.

11. A circuit a-s in claim 10 in which the second resistor provides acertain time-constant for the discharge of the control capacitor and inwhich the second auxiliary capacitor is charged With approximately thesame timeconstant.

12. A circuit as in claim 10 in which thte second auxiliary capacitor ischarged through the second and third resistors in series.

13. A circuit as in claim 10 in which the device is capacitively shuntedby the auxiliary capacitors in series.

14. A circuit as in claim 10 in which the second auxiliary capacitor ischarged through only the third of the resistors,

15. A circuit as in claim 10 in which the device is capacitively shuntedby only the first of the auxiliary capacitors.

References Cited UNITED STATES PATENTS 2,957,074 10/1960 Trevor 325-415X 2,958,027 10/1960 Moseley et al 320-1 X 3,021,489 2/1962 Nielsen330-141 X 3,109,989 11/1963 Muir 325-415 X 3,110,864 11/1963 Smith-Vanizet al. 325-411 X 3,165,699 l/1965 Henmueller 325-411 X 3,333,208 7/1967Hudak 330-141 X LEE T. HIX, Primary Examiner A. D. PELLINEN, AssistantExaminer U.S. Cl. X.R.

